The Land of Nod has a post about one of my favorite wild ideas, the root races of Madame Blavatsky. I have Blavatsky's Secret Doctrine somewhere, but I've only dug partway through the first chapter or two and also through the section on root races; Blavatsky is not a writer of sparkling skill. But I always liked the root races because of their influence on science fiction and fantasy. Matthew mentions the resemblance of the egg-laying Shalmalians to the people of Barsoom; in fact, Edgar Rice Burroughs was involved with Theosophy, so it's assumed he was deliberately playing with the ideas. However, I think he mainly used the Atlanteans as the framework for the red, yellow, black, and white martians and transformed the much taller Shalmalians into the green martians.
Another author who mentions reading Blavatsky is Lovecraft, who uses the past and future root races of man as different forms taken by the Great Race in their migration through time ("The Shadow Out of Time".)
Anyway, Matthew has some brief useful write-ups of the root races. Check 'em out.